| Martensitic
Stainless Steel
The most common martensitic alloys, i.e., Alloy 410,
have a moderate chromium content of 12-18% with low
Ni but, more importantly, have a relatively high carbon
content. The principle difference compared with welding
the austenitic and ferritic grades of stainless steel
is the potentially hard HAZ martensitic structure and
the matching composition weld metal. The material can
be successfully welded providing precautions are taken
to avoid cracking in the HAZ, especially in thick section
components and highly restrained joints.
Avoiding weld imperfections –
High hardness in the HAZ makes this type of stainless
steel very prone to hydrogen cracking. The risk of cracking
generally increases with the carbon content. Precautions
must be taken to minimize the risk by: using low hydrogen
process (TIG or MIG) and ensuring the flux or flux coated
consumable are dried (MMA and SAW) according to the
manufacturer's instructions; preheating to around 200
to 300°C — the actual temperature will depend
on weld (especially Cr and C content), section thickness,
and the amount of hydrogen entering the weld metal;
maintaining the recommended minimum interpass temperature;
and carrying out post-weld heat treatment, i.e., at
650-750°C. The time and temperature will be determined
by chemical composition.
Thin section, low carbon material, typically
less than 3 mm, can often be welded without preheat,
providing that a low hydrogen process is used, the joints
have low restraint, and attention is paid to cleaning
the joint area. Thicker section and higher carbon (>0.1%)
material will probably need preheat and post-weld heat
treatment. The post-weld heat treatment should be carried
out immediately after welding not only to temper (toughen)
the structure but also to enable the hydrogen to diffuse
away from the weld metal and HAZ.
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